The subject matter described herein relates generally to wind turbines and, more particularly, to a method and system for selecting wind turbine generators in a wind park for curtailment of output power to provide a wind reserve.
Generally, a wind turbine includes a turbine that has a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.
Some wind turbine configurations include double-fed induction generators (DFIGs). Such configurations may also include power converters that are used to convert a frequency of generated electric power to a frequency substantially similar to a utility grid frequency. Generally there can be two converters, a line-side converter and a rotor converter that are connected by a direct current (DC) link. Moreover, such converters, in conjunction with the DFIG, also transmit electric power between the utility grid and the generator as well as transmit generator excitation power to a wound generator rotor from one of the connections to the electric utility grid connection. Alternatively, some wind turbine configurations include, but are not limited to, alternative types of induction generators, permanent magnet (PM) synchronous generators and electrically-excited synchronous generators and switched reluctance generators. These alternative configurations may also include power converters that are used to convert the frequencies as described above and transmit electrical power between the utility grid and the generator.
A wind park is comprised of a plurality of wind turbine generators operating somewhat in a defined geographic area. Generally, the power produced by the turbines in the wind park is stepped up or stepped down in voltage by one or more transformers in a substation site and transmitted over an electrical grid to various loads. The wind park may include other systems and devices such as a control system, a metrology site, plant lighting and power, and the like. In some instances, the wind park has a power setpoint that is generally less than the summation of the possible power output of all the wind turbine generators that comprise the wind park and are operating, where possible power output is the power that a turbine could produce at that time. Generally, the possible power output for a turbine can be estimated based on wind speed and a reference power curve of the turbine. This difference between the setpoint and the summation of the possible output may be known as a wind reserve. For example, if the summation of possible power output of all of the operating wind turbine generators in a wind park is 100 megawatts (MW), but the setpoint of the wind park is 90 MW, then the wind park has a 10 MW or a 10 percent wind reserve. The wind reserve can be used when wind turbines are down for maintenance or perhaps during emergency generation greater than the normal wind park power setpoint. Generally, when a wind park is curtailed, all of the wind turbines that comprise the park are curtailed. For example, considering the 100 MW wind park described above, if the wind park was comprised of 100, 1-MW wind turbines, then all 100 of the wind turbines would be curtailed by 10 percent. In other words, each of the 100 wind turbines would be allowed to produce 0.9 MW rather than the possible power output of 1 MW. However, this method of curtailing the wind turbines of a wind park requires all of the affected wind turbines to continuously move their pitch systems, which can escalate maintenance requirements and costs. Furthermore, certain wind turbines that comprise the wind park may be better candidates for curtailment than others for various reasons.
Therefore, what are desired are methods and systems that overcome challenges in the art, some of which are described above.